Method and apparatus for providing a substrate with viscous medium

ABSTRACT

Solder paste application, inspection and correction. Following or during application of solder paste on a substrate, the result thereof is inspected and any detected errors are registered. Following an evaluation as to whether correction of these errors is required and if it would be worthwhile, the errors are corrected. The correction involves removing solder paste from locations where so required, and jetting of additional solder paste to locations where so required.

This application is a divisional of co-pending application Ser. No.09/902,110 filed on Jul. 11, 2001, the entire contents of which arehereby incorporated by reference and for which priority is claimed under35 U.S.C. §120.

TECHNICAL FIELD OF THE INVENTION

The present invention generally relates to the field of providingsubstrates with viscous medium. More specifically, the invention relatesto a method of providing a substrate with viscous medium, acorresponding apparatus, an apparatus for correcting application errorsin connection with the application of viscous medium on a substrate, anda method for correcting application errors.

BACKGROUND OF THE INVENTION

In the field of electronics production, it is well known that possiblesources of errors are the electronic circuit boards. Mainly, theseerrors originate from the application of viscous medium, e.g. solderpaste, prior to the mounting of components on the board. Over the years,a number of different techniques have been proposed for detecting errorsresulting from solder paste application. Originally, this detection wasperformed manually. Lately, however, the use of cameras in combinationwith image processing have become the preferred choice for detectingsaid errors. An example of this can be found in the International PatentPublication WO 00/42381, which discloses a method and a device forcontactless inspection of objects on a substrate.

When errors resulting from the application of solder paste have beendetected, and preferably identified, appropriate action must ensue.Traditionally, a board containing errors as a result of the applicationof solder paste is simply taken out of the process. The removed boardcan then be discarded or, commonly, cleaned and subsequently reinstatedat the beginning of the process. Recently, the results of the solderpaste application, i.e. critical parameters thereof, are monitored anderrors are identified, and the monitored parameters are fed back so thatappropriate measures can be taken. This is common in state-of-the-artscreen printing applications.

This feedback can, in the simplest case, be a warning message when aparameter has crossed a certain pre-set limit. The operator can thendecide which actions to take. On the other hand, an advanced systemcould incorporate artificial intelligence to adjust applicationparameters such as, in the case of screen printing, squeegee pressure,speed and angle, amount of paste on the stencil, cleaning interval, etc.Thus, critical process parameters can be monitored and adjusted so thatthe application errors can be reduced. However, the specific boardcontaining the detected errors is dealt with in the traditional mannerdescribed above, i.e. the faulty board is removed from the entireprocess.

When using conventional dispensing, i.e. contact dispensing, as opposedto screen printing for the application of solder paste, dispensing headswith integrated measurement capabilities, for measuring the result ofthe application of solder paste, are known within the art. The measuredparameters can be fed back for process control in order to reduce futureerrors. Since the integrated measurement capabilities can measure thesolder paste application of a single dot, e.g. immediately following thedispensing of said dot, process parameters can be altered for thesubsequent dispensing of dots on the same board. Thereby, small errorscan be detected and process parameters adjusted so that, in the bestcase, major errors requiring the board to be removed from the process,can be avoided.

SUMMARY OF THE INVENTION

Thus, an object of the present invention is to provide a solution to theabove-mentioned problems and to provide an improved productionefficiency.

This and other objects are achieved according to the present inventionby providing an apparatus and a method as will be described below.

In general terms, the invention is based on the insight of theadvantageous results that can be obtained by using correction measuresin relation to the application of viscous medium on a substrate.

According to a first aspect of the invention, there is provided a methodof providing a substrate with viscous medium, comprising the steps ofapplying said viscous medium onto the substrate, inspecting the resultsof said application, determining errors of the application based on saidinspection, and correcting at least some of said errors.

According to a second aspect of the invention there is provided a systemor an apparatus for providing a substrate with a viscous medium,comprising an applicator for applying the viscous medium onto thesubstrate, an inspection device for inspecting the results of saidapplication, a processor for determining application errors based onsaid inspection, and correction device for correcting at least some ofsaid errors.

According to a third aspect of the invention there is provided anapparatus for correcting application errors in connection withapplication of a viscous medium on a substrate, said apparatuscomprising a processor adapted to receive information of said errors inthe application of said viscous medium, and a correction device forcorrecting at least some of said errors based on said information.

According to a fourth aspect of the present invention, there is provideda method of correcting application errors in regard to viscous mediumprovided on a substrate, comprising the steps of providing a jettingdevice, and using said jetting device for correcting said errors.

For the purposes of this application, it is to be noted that the term“viscous medium” should be interpreted as solder paste, flux, adhesive,conductive adhesive, or any other kind of medium used for fasteningcomponents on a substrate, or resistive paste; and that the term“substrate” should be interpreted as a printed circuit board (PCB), asubstrate for ball grid arrays (BGA), chip scale packages (CSP), quadflat packages (QFP), and flip-chips or the like. It is also to be notedthat the term “jetting” should be interpreted as a non-contactdispensing process that utilises a fluid jet to form and shoot dropletsof a viscous medium from a jet nozzle onto a substrate, as compared to acontact dispensing process, such as “fluid wetting”, which is the act ofthe viscous medium leaving the dispense tip, contacting and clinging tothe substrate and remaining on the substrate as the dispense tip pullsaway.

Preferably, use is made of a jetting device and/or a removing device forthe correction of errors resulting from the application of a viscousmedium on a substrate. Said correction is performed after theapplication of said viscous medium, but prior to any soldering thereof.Preferably, said correction is also performed prior to the mounting ofcomponents, at the locations on the substrate where correction isrequired. It must, however, be noted that the correction of said errorscan be performed after mounting of components at other locations on thesubstrate. This is for instance the case when mounting components onboth sides of a substrate. Then, correction of errors according to thepresent application can be performed at one side after components havebeen mounted and attached to the other side of the substrate.

Thus, the correction of viscous medium applied on a substrate accordingto the present invention must not be mistaken for the known correctionof soldered connections, which is performed late in the componentmounting cycle after the mounting of components and hardening of theviscous medium, i.e. reflow of solder paste, used for mechanically andelectrically connecting the component to the substrate. An advantage ofcorrecting errors prior to the mounting of components and hardening ofthe viscous medium is that it is much cheaper, as compared to makingcorrections late in the mounting process cycle. This is due to the factthat valuable production capacity is not occupied by a substrate thatmust be corrected. Further, correction performed prior to the mountingof components is easier and requires less correction steps.

According to the present invention, said application of viscous mediumis not intended to be limited to a particular method of applying viscousmedium, i.e. application through e.g. screen printing, conventionaldispensing, jetting, etc. On the contrary, the present invention isintended to be applicable for the correction of any substrate that isprovided with a viscous medium, regardless of how the viscous medium wasoriginally applied.

According to one embodiment of the present invention, following theapplication of viscous medium on a substrate, the result of saidapplication is inspected. This inspection can be performed after thecompletion of the application of viscous medium on the entire substrate,or can be performed during said application, e.g. at intermittentintervals or continuously, depending on the application method beingused. When applying the viscous medium through screen printing, theinspection is preferably performed when the application is completed.When applying viscous medium through contact dispensing or jetting, theinspection can be performed following the dispensing of viscous mediumat each specific site or position, or at certain predeterminedintervals.

The inspection not only detects whether a site or position has beenprovided with viscous medium, but also detects whether the correctamount, i.e. volume, of viscous medium has been applied, whether theposition of the applied medium is correct, or within a predeterminedfault range, and has the correct shape and height at a given position.The term “correct” has here the meaning of the measured parameter beingwithin a fault range that is predetermined.

According to alternative embodiments of the invention, the inspectioncould involve inspection of the entire substrate, all locations on thesubstrate where viscous medium is to be applied, or only specificlocations on the substrate. The latter would preferably involveinspecting specific locations that are particularly error prone, e.g.locations where components are later to be placed which are particularlysensitive to errors in the applied viscous medium, such as componentshaving leads with a very fine pitch, or components which are difficultto inspect after soldering, such as BGA components.

According to an embodiment of the invention, following the detection ofan error, the characteristics of said detected error are determined andstored. Preferably, the error characteristics are further analysed andevaluated to determine whether the error needs correcting. If so, theproper method of correcting said error is also determined. According toan embodiment, the time needed for performing said correction isestimated and stored.

According to an embodiment of the invention, the application of viscousmedium is performed through screen printing. Following the completion ofthe screen printing, the result of the screen printing is inspected andany errors are detected, determined, and analysed. The results of saidinspection can be fed back to the screen printer for enabling the screenprinter to correct or adjust parameters. Following the inspection anddetermination of errors, correction of the determined errors ensues.

According to another embodiment of the invention, the application ofviscous medium is performed using conventional contact dispensing orjetting. This enables continuous, on-line inspection of the results ofsaid application. Thus, the application of viscous medium at a singlelocation can be immediately inspected, e.g. dot by dot, or deposit bydeposit, and the results can both be fed back for adjustment ofdispensing or jetting parameters, or can be immediately transferred to adevice for correcting any detected errors. According to an alternativeembodiment, the inspection is performed following the completion of theapplication of viscous medium on the entire substrate. Then, and asdescribed above, the inspection could involve inspecting the entiresubstrate, all locations on the substrate where viscous medium is to beapplied, or predetermined specific locations on the substrate.

According to the present invention, the correction of determined errorson a substrate is performed by the use of jetting for applyingadditional viscous medium. Not only is jetting faster, jetting is alsomore accurate and more flexible in comparison with conventionaldispensing. The use of conventional dispensing often provide a bottleneck that increases the cycle time in the overall component mountingprocess, as compared to the use of jetting. It has also been found thatit is possible to achieve smaller dots when using jetting than whenusing conventional dispensing. Further, by using jetting, it is possibleto apply dots of viscous medium having differing heights, which isdifficult when using screen printing.

However, at positions where it has been determined that there has beenapplied too much viscous medium, the surplus viscous medium must beremoved. This is performed according to an embodiment of the inventionby the provision of a removing device capable of removing viscous mediumfrom a specific location on the board. Said removal is preferablyperformed through suction of the viscous medium, preferably incombination with heating the viscous medium prior to the suctionthereof. Due to the characteristics of the viscous medium, e.g. solderpaste, the remains on the substrate of viscous medium at a location atwhich removal of the viscous medium has been performed is generallyminute. But, there may be some flux remains left at said locations.However, this is not a problem due to the fact that where cleaning ofthe substrate is performed following the soldering of components, inorder to get rid of deleterious flux that is used when mounting thecomponents, said flux remains will be removed during said cleaning; andin cases where it is not necessary to remove flux following saidsoldering, the flux remains will not be a problem. Thus, additionalcleaning of the substrate following the removal of surplus viscousmedium will not be necessary.

The combination of a jetting device and a removing device for correctingerrors on a substrate provided with viscous medium enables correction ofall types of application errors. These errors may for instance includehaving applied a surplus of viscous medium or insufficient viscousmedium at a given position. Furthermore, the errors may for instanceinclude applying viscous medium at incorrect positions, applying viscousmedium where the result of the viscous medium application is misaligned,applying viscous medium having characteristics deficiencies of somesort, etc.

According to an embodiment of the present invention, the correction oferrors is performed in a separate machine, i.e. the substrate isforwarded to the correction machine following the determination thatcorrection of the result of viscous medium application is required.According to an alternative embodiment, the correction machine alsocomprises the inspection device described above. Then, all substratesare forwarded to the correction machine for inspection and possiblecorrection of detected errors. Preferably, the results of saidinspection are fed back to the machine for allowing adjustment ofapplication parameters.

Said embodiment of having a stand alone correction machine isparticularly useful when the initial application of viscous medium isperformed by screen printing or contact dispensing. Then, the advantagesrelating to screen printing and contact dispensing, as recognised by theman skilled in the art and not further described herein, can be combinedwith the above described advantages of correction of errors throughjetting.

According to an alternative embodiment of the invention, the correctiondevice, i.e. a jetting device for correction and a removing device, areintegrated in the machine for performing the initial application ofviscous medium onto the substrate. Thus, the inspection can be performedcontinuously and any correction of the substrate necessary can be doneinstantly.

Said embodiment of having an integrated machine for both the initialapplication of viscous medium and the ensuing inspection and correctionis particularly useful when the initial application of viscous medium isperformed by jetting. Thus, a single jetting device can be utilised forboth the initial application and the correction. This would facilitatethe construction of the machine and minimise the size of the machine andalso would provide a small footprint, i.e. the overall floor spacerequired for the machine. Alternatively, the correction is performed bya separate jetting device not used for the initial application ofviscous medium. This would decrease the overall time required for theapplication and the possible correction.

Generally, a separate machine for the correction, and possibly also forthe inspection, would increase line length but decrease the overallcycle time for each substrate as compared to an integrated machine asdescribed above incorporating both the initial application of viscousmedium and the subsequent or concurrent correction. Further, anintegrated machine where the initial application is performed throughscreen printing or contact dispensing would have to overcome a number ofconstructional difficulties.

According to a specific embodiment of the present invention, all errorsoccurring on a single substrate following the completion of theapplication of viscous medium, e.g. following screen printing, arejointly analysed and the total amount of corrections needed for theentire substrate is then determined. Thus, it can be determined whetherthe sum of errors are so great that correction of the errors on thesubstrate are not worthwhile. Preferably, it has been determined thetime required for error correction of each detected error requiringcorrection, then the overall correction time for the entire substrate isevaluated. If it is found that correction of the errors on the substrateif not worthwhile, the substrate can be removed from the process andcleaned without any corrections being made.

Thus, the use of jetting for correcting errors resulting from theapplication of viscous medium onto a substrate enables not only errorprevention, which is known through the feedback of inspection results,but also error correction. This guarantees that a low defect level canbe maintained, which in turn results in the main source of failures inthe electronics production is overcome, reducing the production costsconsiderably. This is done without more than a fractional addition oftime required for the overall application of viscous medium on asubstrate.

The above mentioned and other aspects, advantages, and features of theinvention will be more fully understood from the following descriptionof exemplifying embodiments thereof.

BRIEF DESCRIPTION OF THE DRAWINGS

Exemplifying embodiments of the invention will be described below withreference to the accompanying drawings, in which:

FIG. 1 is a block diagram illustrating a typical prior art arrangementfor handling errors resulting from application of viscous medium.

FIGS. 2-5 are block diagrams illustrating arrangements according toalternative embodiments of the present invention.

FIGS. 6-11 are flow charts illustrating alternative embodiments of themethod according to the present invention.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

In the block diagrams of FIGS. 1-5, the thick-lined arrows depict themovement of a substrate through the production line. The dashed boxessimply indicate that the device(s) or apparatus(es) depicted within thebox can be incorporated in a single machine.

With reference to FIGS. 2-11, there is illustrated exemplary embodimentsof the present invention. As to the means or devices used for applyingsolder paste, inspecting the results of said application, removingsolder paste, and component mounting, use can be made of means ordevices which by themselves are known within the art, and theconstructional features of which are also known. Therefore, aconstructional and functional description of each separate means ordevice has been omitted.

With reference to FIG. 1 there is shown a typical prior art arrangementfor handling errors resulting from solder paste application. The solidarrows depict the transportation of a substrate through the arrangement.The substrate is first brought to a machine 2 for application of thesolder paste. Following the application of solder paste, the substrateis brought to an inspection device 3 where the result of the applicationis inspected. When the application is performed through contactdispensing or jetting, the inspection could take place simultaneouslywith the application. Then, of course, the applicator 2 and theinspection device 3 are incorporated in a single machine 1. If theinspection shows that the result of the solder paste application issatisfactory, then the substrate is conveyed to a component mountingmachine 5. If not, then the substrate is taken out of the productionline, either discarded or cleaned in a cleaning machine 4 and reinstatedin the production line prior to the application machine 2.

There will now be described with reference to FIGS. 2 and 6, a firstembodiment of the present invention for correcting errors resulting fromsolder paste application. A substrate is first brought to an applicationand inspection machine 10, incorporating both an applicator 12 and aninspection device 14. A conventional method of application is used andtherefore not further described. As can be seen from the flow chart inFIG. 6, solder paste is applied to the substrate at 102. Then theinspection of the application result commences at 104 by indicating thestarting point for the inspection. The solder paste application isinspected for a position N at 106. At 108, it is determined whether anerror is detected for position N and, if so, the parameters of thedetected error, e.g. size of solder paste dot, dot position, dot shape,etc., is recorded and, possibly, also fed back to the applicator at 109.At 110, there is a check whether all positions to be inspected have beeninspected. If not, the position parameter N is incremented and the nextposition is inspected at 106.

Following the inspection for all selected positions, the parameters areevaluated at 112 to determine whether correction of the substrate isrequired. If not, the substrate is transferred at 113 to a componentmounting machine 18. However, if correction is required, then the totalamount of correction needed is calculated at 114. The result of thiscalculation is defined as a correction value, which at 116 is comparedto a threshold value for determining whether correction of the substrateis worthwhile. That is, if there are vast correction actions required,then it might be more economical to simply discard the substrate. Thisis of course dependent on the type of substrate and the cost involvedfor the substrate. If correction is deemed worthwhile, then thesubstrate is transferred at 118 to a correction machine 16. Thecorrection machine 16 incorporates both a device for removing surplussolder paste, as well as a jetting device for jetting additional solderpaste onto the substrate.

As is understood by the man skilled in the art, the above-mentionedsteps of recording, evaluating, determining and sending and retrievinginformation can be performed by the use of a conventional processor (notshown).

Turning now to FIGS. 3 and 7, there is illustrated a second exemplaryembodiment of the present invention. The invention according to thisembodiment differs from the first embodiment in that the applicator 22is not incorporated with the inspection device 24. Instead, theinspection device 24 can be incorporated with a correction device 26 ina combined inspection and correction machine 20. As is shown in the flowchart of FIG. 7, in this exemplary method 200 the substrate istransferred to the applicator 22 at 202 and provided with solder paste.Then, the substrate is at 204 transferred to the inspection andcorrection machine 20. The inspection device 24 inspects at 208 thesolder paste application result for position N.

At 210 it is determined whether the inspection for position N revealsthat an error that require correction is detected. If so, the error iscorrected by the correction device 26 at step 211. At 212 it is checkedwhether all positions have been inspected. If so, the substrate istransferred at 214 to the component mounting machine 18. For ease ofdescription, it is indicated in FIG. 7 that the correction for positionN is performed directly following the inspection for position N.

However, the inspection device 24 might perform an inspection fasterthan the correction device 26 can perform the corresponding correction.In reality, the inspection is performed as fast as possible, and theinformation as to which positions require correction, and whichcorrection that is needed, is continuously transmitted to the correctiondevice 26. Thus, the inspection device 24 does not wait at a specificposition for the correction device to finish correcting at thatposition. This applies equally for the embodiment of FIGS. 5 and 11,which will follow.

Turning now to FIGS. 4 and 5, there is shown two alternative embodimentswhere the initial application of solder paste is performed with ajetting device 32, 40. In the embodiment of FIG. 4, there are providedtwo separate jetting devices, one for the initial solder pasteapplication, and one included in the correction device 36 for thecorrectional jetting of additional solder paste. In the embodiment ofFIG. 5, the same jetting device is used for both the initial solderpaste application, and for the correctional jetting of additional solderpaste. Thus, the applicator, inspection device and correction device areall integrated in one machine 40.

The method 300 for the arrangement illustrated by FIGS. 4, 8 and 9differs from the methods of FIGS. 6 and 7 in that the application foreach position can be essentially immediately inspected. Turning to FIGS.8 and 9, solder paste is applied through a jetting device 32 forposition N at step 304. The result of the application is then inspectedby the inspection device 34 at step 306. If correction is required,determined at 308, the correction parameters is relayed to thecorrection device 36 at step 309. The application and inspection thencontinues at 304 and 306 until solder paste have been applied and theinspection have been performed for all positions, determined at 310.Simultaneously with said application and inspection, the correctiondevice 36 performs correction of the detected errors at 322 based oninformation received at 320. After each correction has been completed, asignal indicative thereof is transmitted at step 324 to a processor (notshown). At step 310, it is also determined whether all corrections havebeen completed before the substrate is transferred to the componentplacement machine 18 at step 312.

Turning finally to FIGS. 5, 10 and 11, there are illustrated twoalternative methods 400, 500 according to alternative embodiments of thepresent invention. As described above, a single jetting device is usedfor both the initial application of solder paste and the subsequentpossible corrective jetting of additional solder paste. In FIG. 10 thereis shown an alternative where the corrective jetting is performedfollowing the completion of the initial application, whereas in FIG. 11there is shown an alternative where the jetting correction is performedas soon as an error has been detected. As obvious to the man skilled inthe art, any combination of these two alternatives is also possible.

The initial steps 402-410 of method 400 correspond closely to theinitial steps 102-110 of method 100, as shown in FIG. 6. However,following the completion of the initial solder paste application and theinspection and recording of errors, correction of the detected errors isperformed by the correction device, both where additional jetting isrequired as well as the removal of solder paste. According to FIG. 10,for ease of illustration, this is performed by resetting the positionparameter N, at 412 and looping through all positions on the substrateand correcting them in order, at 414-420. However, any type ofcorrection algorithm can be used. Finally, the substrate is transferredat 422 to the component mounting machine 18.

The method 500 shown in FIG. 11 correspond to the method 300 of FIG. 8for all steps 502-512, except for step 509. In method 500 the requiredcorrection is performed at step 509, whereas at step 309 of the method300, parameters are transmitted to a separate correction device.However, as stated above, the correction for a specific position doesnot necessarily take place immediately following the inspection of thatposition.

Even though the invention has been described above using exemplifyingembodiments thereof, alterations, modifications and combinationsthereof, as understood by those skilled in the art, may be made withinthe scope of the invention, which is defined by the accompanying claims.

1. A method of providing a substrate with viscous medium, comprising thesteps of: applying the viscous medium onto the substrate at a pluralityof locations; inspecting the results of said application at more thanone of the plurality of locations after completion of the application atthe plurality of locations; determining errors of the application basedon said inspection; and correcting at least some of said errors.
 2. Themethod as claimed in claim 1, wherein the step of determining errorscomprises the step of evaluating all of the determined errors anddeciding to what extent the determined errors shall be corrected.
 3. Themethod according to claim 1, wherein the step of determining errorsfurther comprises the step of evaluating each of the determined errorsand deciding on proper corrective action.
 4. The method according toclaim 3, wherein the step of determining errors comprises the steps of:estimating for each of the determined errors the time required forperforming said corrective action; and calculating the overall timerequired for corrective action of all determined errors.
 5. The methodaccording to claim 1, wherein said correction comprises jetting ofadditional viscous medium onto the substrate and/or removing viscousmedium from the substrate.
 6. The method according to claim 5, whereinthe step of correcting comprises the step of removing viscous mediumfrom positions on the substrate where viscous medium has beenunintentionally applied.
 7. The method according to claim 5, wherein thestep of correcting comprises the step of removing surplus viscous mediumfrom positions on the substrate where more viscous medium has beenapplied than intended.
 8. The method according to claim 5, wherein thestep of correcting comprises the step of jetting of additional viscousmedium to positions on the substrate where no viscous medium has beenapplied even though intended.
 9. The method according to claim 5,wherein the step of correcting comprises the step of jetting ofadditional viscous medium to positions on the substrate where the amountof applied viscous medium is insufficient.
 10. The method according toclaim 8, further comprising the steps of: inspecting the results of saidjetting of additional viscous medium; determining errors of said jettingof additional viscous medium based on said inspection; and correcting atleast some of said errors.
 11. The method according to claim 9, furthercomprising the steps of: inspecting the results of said jetting ofadditional viscous medium; determining errors of said jetting ofadditional viscous medium based on said inspection; and correcting atleast some of said errors.
 12. The method according to claim 1, whereinthe step of applying viscous medium is performed by jetting.
 13. Themethod according to claim 5, wherein the step of applying viscous mediumis performed by jetting and wherein the application of the viscousmedium and the jetting of additional viscous medium is performed by thesame jetting device.
 14. The method according to claim 1, wherein thestep of applying viscous medium is performed by screen printing.
 15. Themethod according to claim 1, wherein the step of applying viscous mediumis performed by contact dispensing.
 16. The method according to claim 1,wherein said step of correcting is performed after said step of applyingviscous medium has been completed.
 17. The method according to claim 1,wherein said step of inspecting is performed after said step of applyingviscous medium has been completed.
 18. The method according to claim 1,wherein said step of inspecting and said step of correcting areperformed simultaneously after said step of applying viscous medium. 19.The method according to claim 1, wherein said step of correcting isperformed simultaneously with said step of applying viscous medium. 20.The method according to claim 1, wherein said step of inspecting isperformed simultaneously with said step of applying viscous medium. 21.Method of correcting application errors in regard to viscous mediumprovided on a substrate, comprising the steps of: providing a jettingdevice; and using said jetting device for correcting said errors.